A number of different wireless communication techniques have been developed. One common technique used in wireless communication is code division multiple access (CDMA) signal modulation in which multiple communications are simultaneously transmitted over a spread spectrum radio-frequency (RF) signal. Some example wireless communication devices that have incorporated CDMA technology include cellular radiotelephones, PCMCIA cards incorporated within portable computers, personal digital assistants (PDAs) equipped with wireless communication capabilities, and the like.
In CDMA technology and other spread spectrum wireless communication technologies, maximizing system capacity, in terms of the number of simultaneous wireless transmissions that can be handled by the system, is of paramount concern. System capacity in a spread spectrum system, such as a CDMA system, can be maximized by carefully controlling the transmit power of each wireless communication device (WCD). In particular, the transmit power is controlled such that each transmitted signal arrives at a base station receiver at the same optimal power level. Similarly, the transmit power of the base station can be controlled so as to transmit the spread spectrum signal from the base station at an optimal power level.
For example, if a signal transmitted by a WCD arrives at the base station receiver at a power level that is too low, the bit-error-rate may be too high to permit high quality communication with that WCD. On the other hand, if the signal sent from the WCD is at a power level that is too high when received at the base station, the high power signal could interfere with communication between the base station and other WCDs in the system. This interference can adversely affect communications with the other WCDs in the system, thus reducing system capacity. For this reason, to maximize system capacity, it is highly advantageous to control signal power of transmitted signals from each WCD such that the signal can be received by the base station at or near a common optimal power level. Similarly, it is highly advantageous to control signal power of transmitted signals from the base station to one or more WCDs.
A forward link (sometimes referred to as a “downlink”) refers to a signal sent from the base station to the WCD. A reverse link (sometimes referred to as an “uplink”) refers to a signal sent from the WCD to the base station. The forward link from the base station to the WCD typically operates on a different frequency than the reverse link from the WCD to the base station. However, because the forward link and reverse link frequencies are typically within the same frequency band, a significant correlation between power loss in the forward and reverse links typically exists.
For this reason, power control in a WCD, for example, is sometimes implemented by estimating the received power in the forward link and then adjusting power transmission over the reverse link accordingly. For example, the WCD can estimate received power from the base station and compare the estimate to a target power level. If the estimate is less than the target power level, the WCD can increase its transmit power accordingly. If the estimate is greater than the target, the WCD can decrease its transmit power accordingly. In this manner, an estimate of received power in the WCD can be used to effectively control transmit power from the WCD. The base station may implement power control in a similar manner.
Another power control technique involves estimating received power and comparing the estimation to a target, before sending a command signal back to the device that sent the original signal. In other words, a base station can estimate received power from a WCD, compare the received power to a target, and transmit a command back to the WCD to control transmit power from the WCD. The command may take the form of one or more power control bits that direct the WCD to increment or decrement the level of transmit power. Similarly, the WCD can estimate received power from the base station, compare the received power to a target, and transmit a power control command back to the base station to control transmittal power from the base station. Thus, the base station and WCD can effectively communicate with one another to periodically adjust one another's transmission power so as to achieve more optimal power levels in the system.
Generating an optimal estimate of received power, however, can be very complex. For this reason, sub-optimal estimations are commonly used to provide adequate power estimations using less intensive computational techniques. Still, to the extent estimations of received power can be improved, system performance and capacity can likewise be improved.